The invention relates to measuring and testing torque using a dynamometer with a rotating torque responsive element, but more particularly, the invention relates to apparatus for dynamically testing power transmission belts.
Four-square testing apparatus is used to determine the dynamic effect of horsepower and torque on power transmission components. In such apparatus, power is recirculated between two rotating shafts. The advantage of such drives is that input power is quite small compared to the power absorbed in the recirculating system. The input power need make up only for power losses of the system.
Preload torque in known quantity is easily introduced in apparatus where the shafts are mechanically interlocked with positive rotational devices such as gears. Starting with parallel shafts mechanically interconnected with spur gears, one shaft may be rotationally displaced from the other to preload a known torque in the two shafts. Rotation of either shaft by external means causes the preload torque to be dynamically recirculated between the two rotating shafts. While such apparatus is satisfactory for testing power transmission components where the shafts are mechanically interlocked, the apparatus is unsatisfactory for testing power transmission components where mechanical interlocking of the two shafts cannot be obtained. The apparatus is unsatisfactory for testing components which transmit power by means of friction. This is because the statically introduced torque is easily lost at the friction surfaces, leaving no preload for power recirculation.
In a type of four-square apparatus, it is known to have two parallel shafts with two pulleys of different diameters mounted on each shaft. The pulleys are arranged so the large pulley of one shaft is aligned with the smaller pulley of the other shaft. The difference in pulley diameters is chosen for a predetermined speed ratio. Two V-belts are arranged over the pulleys and preloaded. One shaft is rotated. The difference in speed ratio causes power to recirculate between the belts. A problem associated with such a device is that of determining the tension in each belt. This is because belts typically stretch and wear down in width during their normal service life and they are built with circumferential tolerances. While the torque between two belts could be measured, their contribution and their share of a recirculating horsepower load is indeterminate because of the unknown tensions. Also, the torque arising from a given ratio cannot be predicted ahead of time because of variations in belt transverse and longitudinal elastic characteristics.
Another problem with such a device is that the speed ratio between shafts is fixed. Only one horsepower/torque level may be tested at a time. The pulleys must be removed and changed with different diameter pulleys to effect different points of horsepower and torque.
A solution of the problem of separating known quantities of tension and torque in a V-belt test apparatus is presented in Canadian Pat. No. 963,690 to Miller et al. (U.S. Pat. No. 3,739,632). First and second shafts are coaxially arranged and tied together through a torque applicator. The torque applicator may be in the form of a hydraulic motor or other mechanism that imparts relative rotation between the coaxial shafts. Third and fourth shafts are spaced from and arranged parallel to the first and second shafts. The third and fourth shafts are parallelly displaced from each other within the confines of a device known as a "Schmidt" coupling. Pulleys are arranged at the free ends of the shafts and V-belts are arranged over the pulleys. One shaft is rotated while the torque applicator imparts relative rotation between the shafts. The problem associated with this type of device is that four shafts must be used with complicated interconnecting devices which consume power and space.